The proton adsorption properties of clay particles

M. AVENA

University of Tsukuba, Japón

Jornada; Seminar on Colloids and Interfaces in Environments; 2008

University of Tsukuba

Clay minerals are formed by very thin unit layers caller phyllosilicate layers. They are so thin that around 40% of their constituting atoms are located at the surface. These surface atoms may become very active in binding ions and molecules from the surrounding medium giving rise to the important adsorptive properties of clays.             This talk discusses the points that have more impact in the protonation-deprotonation behavior of a phyllosilicate clay surface in aqueous media. Proton binding at a phyllosilcate clay surface takes place at oxygen-containing groups. The protonation behavior depends on the intrinsic affinity of surface groups and long-range electrostatics. The application of the MUSIC model confirms that the proton affinity of siloxane and gibbsite-like groups located at the basal surfaces (001 planes) of 2:1 or 1:1 clays are very low. On the contrary, the proton affinity of surface groups at the broken edges is adequate to undergo protonation-deprotonation reactions in a normal pH range. It is also shown that the reactivity of edge groups is affected by the presence of structural charges within the clay layer. As a consequence of this effect, the point of zero charge of the edges depends on the supporting electrolyte concentration, decreasing as the electrolyte concentration increases.             Some models of the clay water interface are discussed and compared, and the proton adsorption properties of phyllosilicate clays are modeled.